package fifthtest;

import java.util.AbstractSequentialList;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Deque;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;




public class LinkedList<E>

    extends AbstractSequentialList<E>

    implements List<E>, Deque<E>, Cloneable, java.io.Serializable

{

    transient int size = 0;



    transient Node<E> first;


    

    transient Node<E> last;



    public LinkedList() {

    }


   

    public LinkedList(Collection<? extends E> c) {

        this();

        addAll(c);

    }



    private void linkFirst(E e) {

        final Node<E> f = first;

        final Node<E> newNode = new Node<>(null, e, f);

        first = newNode;

        if (f == null)

            last = newNode;

        else

            f.prev = newNode;

        size++;

        modCount++;

    }


    
    void linkLast(E e) {

        final Node<E> l = last;

        final Node<E> newNode = new Node<>(l, e, null);

        last = newNode;

        if (l == null)

            first = newNode;

        else

            l.next = newNode;

        size++;

        modCount++;

    }


  

    void linkBefore(E e, Node<E> succ) {

        // assert succ != null;

        final Node<E> pred = succ.prev;

        final Node<E> newNode = new Node<>(pred, e, succ);

        succ.prev = newNode;

        if (pred == null)

            first = newNode;

        else

            pred.next = newNode;

        size++;

        modCount++;

    }


    /**

     * Unlinks non-null first node f.

     */

    private E unlinkFirst(Node<E> f) {

        // assert f == first && f != null;

        final E element = f.item;

        final Node<E> next = f.next;

        f.item = null;

        f.next = null; // help GC

        first = next;

        if (next == null)

            last = null;

        else

            next.prev = null;

        size--;

        modCount++;

        return element;

    }


    /**

     * Unlinks non-null last node l.

     */

    private E unlinkLast(Node<E> l) {

        // assert l == last && l != null;

        final E element = l.item;

        final Node<E> prev = l.prev;

        l.item = null;

        l.prev = null; // help GC

        last = prev;

        if (prev == null)

            first = null;

        else

            prev.next = null;

        size--;

        modCount++;

        return element;

    }


    /**

     * Unlinks non-null node x.

     */

    E unlink(Node<E> x) {

        // assert x != null;

        final E element = x.item;

        final Node<E> next = x.next;

        final Node<E> prev = x.prev;


        if (prev == null) {

            first = next;

        } else {

            prev.next = next;

            x.prev = null;

        }


        if (next == null) {

            last = prev;

        } else {

            next.prev = prev;

            x.next = null;

        }


        x.item = null;

        size--;

        modCount++;

        return element;

    }


    /**

     * Returns the first element in this list.

     *

     * @return the first element in this list

     * @throws NoSuchElementException if this list is empty

     */

    public E getFirst() {

        final Node<E> f = first;

        if (f == null)

            throw new NoSuchElementException();

        return f.item;

    }


    /**

     * Returns the last element in this list.

     *

     * @return the last element in this list

     * @throws NoSuchElementException if this list is empty

     */

    public E getLast() {

        final Node<E> l = last;

        if (l == null)

            throw new NoSuchElementException();

        return l.item;

    }


    /**

     * Removes and returns the first element from this list.

     *

     * @return the first element from this list

     * @throws NoSuchElementException if this list is empty

     */

    public E removeFirst() {

        final Node<E> f = first;

        if (f == null)

            throw new NoSuchElementException();

        return unlinkFirst(f);

    }


    /**

     * Removes and returns the last element from this list.

     *

     * @return the last element from this list

     * @throws NoSuchElementException if this list is empty

     */

    public E removeLast() {

        final Node<E> l = last;

        if (l == null)

            throw new NoSuchElementException();

        return unlinkLast(l);

    }


    /**

     * Inserts the specified element at the beginning of this list.

     *

     * @param e the element to add

     */

    public void addFirst(E e) {

        linkFirst(e);

    }


    /**

     * Appends the specified element to the end of this list.

     *

     * <p>This method is equivalent to {@link #add}.

     *

     * @param e the element to add

     */

    public void addLast(E e) {

        linkLast(e);

    }


    /**

     * Returns {@code true} if this list contains the specified element.

     * More formally, returns {@code true} if and only if this list contains

     * at least one element {@code e} such that

     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.

     *

     * @param o element whose presence in this list is to be tested

     * @return {@code true} if this list contains the specified element

     */

    public boolean contains(Object o) {

        return indexOf(o) != -1;

    }


    /**

     * Returns the number of elements in this list.

     *

     * @return the number of elements in this list

     */

    public int size() {

        return size;

    }


    /**

     * Appends the specified element to the end of this list.

     *

     * <p>This method is equivalent to {@link #addLast}.

     *

     * @param e element to be appended to this list

     * @return {@code true} (as specified by {@link Collection#add})

     */

    public boolean add(E e) {

        linkLast(e);

        return true;

    }


    /**

     * Removes the first occurrence of the specified element from this list,

     * if it is present.  If this list does not contain the element, it is

     * unchanged.  More formally, removes the element with the lowest index

     * {@code i} such that

     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>

     * (if such an element exists).  Returns {@code true} if this list

     * contained the specified element (or equivalently, if this list

     * changed as a result of the call).

     *

     * @param o element to be removed from this list, if present

     * @return {@code true} if this list contained the specified element

     */

    public boolean remove(Object o) {

        if (o == null) {

            for (Node<E> x = first; x != null; x = x.next) {

                if (x.item == null) {

                    unlink(x);

                    return true;

                }

            }

        } else {

            for (Node<E> x = first; x != null; x = x.next) {

                if (o.equals(x.item)) {

                    unlink(x);

                    return true;

                }

            }

        }

        return false;

    }


    /**

     * Appends all of the elements in the specified collection to the end of

     * this list, in the order that they are returned by the specified

     * collection's iterator.  The behavior of this operation is undefined if

     * the specified collection is modified while the operation is in

     * progress.  (Note that this will occur if the specified collection is

     * this list, and it's nonempty.)

     *

     * @param c collection containing elements to be added to this list

     * @return {@code true} if this list changed as a result of the call

     * @throws NullPointerException if the specified collection is null

     */

    public boolean addAll(Collection<? extends E> c) {

        return addAll(size, c);

    }


    /**

     * Inserts all of the elements in the specified collection into this

     * list, starting at the specified position.  Shifts the element

     * currently at that position (if any) and any subsequent elements to

     * the right (increases their indices).  The new elements will appear

     * in the list in the order that they are returned by the

     * specified collection's iterator.

     *

     * @param index index at which to insert the first element

     *              from the specified collection

     * @param c collection containing elements to be added to this list

     * @return {@code true} if this list changed as a result of the call

     * @throws IndexOutOfBoundsException {@inheritDoc}

     * @throws NullPointerException if the specified collection is null

     */

    public boolean addAll(int index, Collection<? extends E> c) {

        checkPositionIndex(index);


        Object[] a = c.toArray();

        int numNew = a.length;

        if (numNew == 0)

            return false;


        Node<E> pred, succ;

        if (index == size) {

            succ = null;

            pred = last;

        } else {

            succ = node(index);

            pred = succ.prev;

        }


        for (Object o : a) {

            @SuppressWarnings("unchecked") E e = (E) o;

            Node<E> newNode = new Node<>(pred, e, null);

            if (pred == null)

                first = newNode;

            else

                pred.next = newNode;

            pred = newNode;

        }


        if (succ == null) {

            last = pred;

        } else {

            pred.next = succ;

            succ.prev = pred;

        }


        size += numNew;

        modCount++;

        return true;

    }


    /**

     * Removes all of the elements from this list.

     * The list will be empty after this call returns.

     */

    public void clear() {

        // Clearing all of the links between nodes is "unnecessary", but:

        // - helps a generational GC if the discarded nodes inhabit

        //   more than one generation

        // - is sure to free memory even if there is a reachable Iterator

        for (Node<E> x = first; x != null; ) {

            Node<E> next = x.next;

            x.item = null;

            x.next = null;

            x.prev = null;

            x = next;

        }

        first = last = null;

        size = 0;

        modCount++;

    }



    // Positional Access Operations


    /**

     * Returns the element at the specified position in this list.

     *

     * @param index index of the element to return

     * @return the element at the specified position in this list

     * @throws IndexOutOfBoundsException {@inheritDoc}

     */

    public E get(int index) {

        checkElementIndex(index);

        return node(index).item;

    }


    /**

     * Replaces the element at the specified position in this list with the

     * specified element.

     *

     * @param index index of the element to replace

     * @param element element to be stored at the specified position

     * @return the element previously at the specified position

     * @throws IndexOutOfBoundsException {@inheritDoc}

     */

    public E set(int index, E element) {

        checkElementIndex(index);

        Node<E> x = node(index);

        E oldVal = x.item;

        x.item = element;

        return oldVal;

    }


    /**

     * Inserts the specified element at the specified position in this list.

     * Shifts the element currently at that position (if any) and any

     * subsequent elements to the right (adds one to their indices).

     *

     * @param index index at which the specified element is to be inserted

     * @param element element to be inserted

     * @throws IndexOutOfBoundsException {@inheritDoc}

     */

    public void add(int index, E element) {

        checkPositionIndex(index);


        if (index == size)

            linkLast(element);

        else

            linkBefore(element, node(index));

    }


    /**

     * Removes the element at the specified position in this list.  Shifts any

     * subsequent elements to the left (subtracts one from their indices).

     * Returns the element that was removed from the list.

     *

     * @param index the index of the element to be removed

     * @return the element previously at the specified position

     * @throws IndexOutOfBoundsException {@inheritDoc}

     */

    public E remove(int index) {

        checkElementIndex(index);

        return unlink(node(index));

    }


    /**

     * Tells if the argument is the index of an existing element.

     */

    private boolean isElementIndex(int index) {

        return index >= 0 && index < size;

    }


    /**

     * Tells if the argument is the index of a valid position for an

     * iterator or an add operation.

     */

    private boolean isPositionIndex(int index) {

        return index >= 0 && index <= size;

    }


    /**

     * Constructs an IndexOutOfBoundsException detail message.

     * Of the many possible refactorings of the error handling code,

     * this "outlining" performs best with both server and client VMs.

     */

    private String outOfBoundsMsg(int index) {

        return "Index: "+index+", Size: "+size;

    }


    private void checkElementIndex(int index) {

        if (!isElementIndex(index))

            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

    }


    private void checkPositionIndex(int index) {

        if (!isPositionIndex(index))

            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

    }


    /**

     * Returns the (non-null) Node at the specified element index.

     */

    Node<E> node(int index) {

        // assert isElementIndex(index);


        if (index < (size >> 1)) {

            Node<E> x = first;

            for (int i = 0; i < index; i++)

                x = x.next;

            return x;

        } else {

            Node<E> x = last;

            for (int i = size - 1; i > index; i--)

                x = x.prev;

            return x;

        }

    }


    // Search Operations


    /**

     * Returns the index of the first occurrence of the specified element

     * in this list, or -1 if this list does not contain the element.

     * More formally, returns the lowest index {@code i} such that

     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,

     * or -1 if there is no such index.

     *

     * @param o element to search for

     * @return the index of the first occurrence of the specified element in

     *         this list, or -1 if this list does not contain the element

     */

    public int indexOf(Object o) {

        int index = 0;

        if (o == null) {

            for (Node<E> x = first; x != null; x = x.next) {

                if (x.item == null)

                    return index;

                index++;

            }

        } else {

            for (Node<E> x = first; x != null; x = x.next) {

                if (o.equals(x.item))

                    return index;

                index++;

            }

        }

        return -1;

    }


    /**

     * Returns the index of the last occurrence of the specified element

     * in this list, or -1 if this list does not contain the element.

     * More formally, returns the highest index {@code i} such that

     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,

     * or -1 if there is no such index.

     *

     * @param o element to search for

     * @return the index of the last occurrence of the specified element in

     *         this list, or -1 if this list does not contain the element

     */

    public int lastIndexOf(Object o) {

        int index = size;

        if (o == null) {

            for (Node<E> x = last; x != null; x = x.prev) {

                index--;

                if (x.item == null)

                    return index;

            }

        } else {

            for (Node<E> x = last; x != null; x = x.prev) {

                index--;

                if (o.equals(x.item))

                    return index;

            }

        }

        return -1;

    }


    // Queue operations.


    /**

     * Retrieves, but does not remove, the head (first element) of this list.

     *

     * @return the head of this list, or {@code null} if this list is empty

     * @since 1.5

     */

    public E peek() {

        final Node<E> f = first;

        return (f == null) ? null : f.item;

    }


    /**

     * Retrieves, but does not remove, the head (first element) of this list.

     *

     * @return the head of this list

     * @throws NoSuchElementException if this list is empty

     * @since 1.5

     */

    public E element() {

        return getFirst();

    }


    /**

     * Retrieves and removes the head (first element) of this list.

     *

     * @return the head of this list, or {@code null} if this list is empty

     * @since 1.5

     */

    public E poll() {

        final Node<E> f = first;

        return (f == null) ? null : unlinkFirst(f);

    }


    /**

     * Retrieves and removes the head (first element) of this list.

     *

     * @return the head of this list

     * @throws NoSuchElementException if this list is empty

     * @since 1.5

     */

    public E remove() {

        return removeFirst();

    }


    /**

     * Adds the specified element as the tail (last element) of this list.

     *

     * @param e the element to add

     * @return {@code true} (as specified by {@link Queue#offer})

     * @since 1.5

     */

    public boolean offer(E e) {

        return add(e);

    }


    // Deque operations

    /**

     * Inserts the specified element at the front of this list.

     *

     * @param e the element to insert

     * @return {@code true} (as specified by {@link Deque#offerFirst})

     * @since 1.6

     */

    public boolean offerFirst(E e) {

        addFirst(e);

        return true;

    }


    /**

     * Inserts the specified element at the end of this list.

     *

     * @param e the element to insert

     * @return {@code true} (as specified by {@link Deque#offerLast})

     * @since 1.6

     */

    public boolean offerLast(E e) {

        addLast(e);

        return true;

    }


    /**

     * Retrieves, but does not remove, the first element of this list,

     * or returns {@code null} if this list is empty.

     *

     * @return the first element of this list, or {@code null}

     *         if this list is empty

     * @since 1.6

     */

    public E peekFirst() {

        final Node<E> f = first;

        return (f == null) ? null : f.item;

     }


    /**

     * Retrieves, but does not remove, the last element of this list,

     * or returns {@code null} if this list is empty.

     *

     * @return the last element of this list, or {@code null}

     *         if this list is empty

     * @since 1.6

     */

    public E peekLast() {

        final Node<E> l = last;

        return (l == null) ? null : l.item;

    }


    /**

     * Retrieves and removes the first element of this list,

     * or returns {@code null} if this list is empty.

     *

     * @return the first element of this list, or {@code null} if

     *     this list is empty

     * @since 1.6

     */

    public E pollFirst() {

        final Node<E> f = first;

        return (f == null) ? null : unlinkFirst(f);

    }


    /**

     * Retrieves and removes the last element of this list,

     * or returns {@code null} if this list is empty.

     *

     * @return the last element of this list, or {@code null} if

     *     this list is empty

     * @since 1.6

     */

    public E pollLast() {

        final Node<E> l = last;

        return (l == null) ? null : unlinkLast(l);

    }


    /**

     * Pushes an element onto the stack represented by this list.  In other

     * words, inserts the element at the front of this list.

     *

     * <p>This method is equivalent to {@link #addFirst}.

     *

     * @param e the element to push

     * @since 1.6

     */

    public void push(E e) {

        addFirst(e);

    }


    /**

     * Pops an element from the stack represented by this list.  In other

     * words, removes and returns the first element of this list.

     *

     * <p>This method is equivalent to {@link #removeFirst()}.

     *

     * @return the element at the front of this list (which is the top

     *         of the stack represented by this list)

     * @throws NoSuchElementException if this list is empty

     * @since 1.6

     */

    public E pop() {

        return removeFirst();

    }


    /**

     * Removes the first occurrence of the specified element in this

     * list (when traversing the list from head to tail).  If the list

     * does not contain the element, it is unchanged.

     *

     * @param o element to be removed from this list, if present

     * @return {@code true} if the list contained the specified element

     * @since 1.6

     */

    public boolean removeFirstOccurrence(Object o) {

        return remove(o);

    }


    /**

     * Removes the last occurrence of the specified element in this

     * list (when traversing the list from head to tail).  If the list

     * does not contain the element, it is unchanged.

     *

     * @param o element to be removed from this list, if present

     * @return {@code true} if the list contained the specified element

     * @since 1.6

     */

    public boolean removeLastOccurrence(Object o) {

        if (o == null) {

            for (Node<E> x = last; x != null; x = x.prev) {

                if (x.item == null) {

                    unlink(x);

                    return true;

                }

            }

        } else {

            for (Node<E> x = last; x != null; x = x.prev) {

                if (o.equals(x.item)) {

                    unlink(x);

                    return true;

                }

            }

        }

        return false;

    }


    /**

     * Returns a list-iterator of the elements in this list (in proper

     * sequence), starting at the specified position in the list.

     * Obeys the general contract of {@code List.listIterator(int)}.<p>

     *

     * The list-iterator is <i>fail-fast</i>: if the list is structurally

     * modified at any time after the Iterator is created, in any way except

     * through the list-iterator's own {@code remove} or {@code add}

     * methods, the list-iterator will throw a

     * {@code ConcurrentModificationException}.  Thus, in the face of

     * concurrent modification, the iterator fails quickly and cleanly, rather

     * than risking arbitrary, non-deterministic behavior at an undetermined

     * time in the future.

     *

     * @param index index of the first element to be returned from the

     *              list-iterator (by a call to {@code next})

     * @return a ListIterator of the elements in this list (in proper

     *         sequence), starting at the specified position in the list

     * @throws IndexOutOfBoundsException {@inheritDoc}

     * @see List#listIterator(int)

     */

    public ListIterator<E> listIterator(int index) {

        checkPositionIndex(index);

        return new ListItr(index);

    }


    private class ListItr implements ListIterator<E> {

        private Node<E> lastReturned = null;

        private Node<E> next;

        private int nextIndex;

        private int expectedModCount = modCount;


        ListItr(int index) {

            // assert isPositionIndex(index);

            next = (index == size) ? null : node(index);

            nextIndex = index;

        }


        public boolean hasNext() {

            return nextIndex < size;

        }


        public E next() {

            checkForComodification();

            if (!hasNext())

                throw new NoSuchElementException();


            lastReturned = next;

            next = next.next;

            nextIndex++;

            return lastReturned.item;

        }


        public boolean hasPrevious() {

            return nextIndex > 0;

        }


        public E previous() {

            checkForComodification();

            if (!hasPrevious())

                throw new NoSuchElementException();


            lastReturned = next = (next == null) ? last : next.prev;

            nextIndex--;

            return lastReturned.item;

        }


        public int nextIndex() {

            return nextIndex;

        }


        public int previousIndex() {

            return nextIndex - 1;

        }


        public void remove() {

            checkForComodification();

            if (lastReturned == null)

                throw new IllegalStateException();


            Node<E> lastNext = lastReturned.next;

            unlink(lastReturned);

            if (next == lastReturned)

                next = lastNext;

            else

                nextIndex--;

            lastReturned = null;

            expectedModCount++;

        }


        public void set(E e) {

            if (lastReturned == null)

                throw new IllegalStateException();

            checkForComodification();

            lastReturned.item = e;

        }


        public void add(E e) {

            checkForComodification();

            lastReturned = null;

            if (next == null)

                linkLast(e);

            else

                linkBefore(e, next);

            nextIndex++;

            expectedModCount++;

        }


        public void forEachRemaining(Consumer<? super E> action) {

            Objects.requireNonNull(action);

            while (modCount == expectedModCount && nextIndex < size) {

                action.accept(next.item);

                lastReturned = next;

                next = next.next;

                nextIndex++;

            }

            checkForComodification();

        }


        final void checkForComodification() {

            if (modCount != expectedModCount)

                throw new ConcurrentModificationException();

        }

    }


    private static class Node<E> {

        E item;

        Node<E> next;

        Node<E> prev;


        Node(Node<E> prev, E element, Node<E> next) {

            this.item = element;

            this.next = next;

            this.prev = prev;

        }

    }


    /**

     * @since 1.6

     */

    public Iterator<E> descendingIterator() {

        return new DescendingIterator();

    }


    /**

     * Adapter to provide descending iterators via ListItr.previous

     */

    private class DescendingIterator implements Iterator<E> {

        private final ListItr itr = new ListItr(size());

        public boolean hasNext() {

            return itr.hasPrevious();

        }

        public E next() {

            return itr.previous();

        }

        public void remove() {

            itr.remove();

        }

    }


    @SuppressWarnings("unchecked")

    private LinkedList<E> superClone() {

        try {

            return (LinkedList<E>) super.clone();

        } catch (CloneNotSupportedException e) {

            throw new InternalError(e);

        }

    }


    /**

     * Returns a shallow copy of this {@code LinkedList}. (The elements

     * themselves are not cloned.)

     *

     * @return a shallow copy of this {@code LinkedList} instance

     */

    public Object clone() {

        LinkedList<E> clone = superClone();


        // Put clone into "virgin" state

        clone.first = clone.last = null;

        clone.size = 0;

        clone.modCount = 0;


        // Initialize clone with our elements

        for (Node<E> x = first; x != null; x = x.next)

            clone.add(x.item);


        return clone;

    }


    /**

     * Returns an array containing all of the elements in this list

     * in proper sequence (from first to last element).

     *

     * <p>The returned array will be "safe" in that no references to it are

     * maintained by this list.  (In other words, this method must allocate

     * a new array).  The caller is thus free to modify the returned array.

     *

     * <p>This method acts as bridge between array-based and collection-based

     * APIs.

     *

     * @return an array containing all of the elements in this list

     *         in proper sequence

     */

    public Object[] toArray() {

        Object[] result = new Object[size];

        int i = 0;

        for (Node<E> x = first; x != null; x = x.next)

            result[i++] = x.item;

        return result;

    }


    /**

     * Returns an array containing all of the elements in this list in

     * proper sequence (from first to last element); the runtime type of

     * the returned array is that of the specified array.  If the list fits

     * in the specified array, it is returned therein.  Otherwise, a new

     * array is allocated with the runtime type of the specified array and

     * the size of this list.

     *

     * <p>If the list fits in the specified array with room to spare (i.e.,

     * the array has more elements than the list), the element in the array

     * immediately following the end of the list is set to {@code null}.

     * (This is useful in determining the length of the list <i>only</i> if

     * the caller knows that the list does not contain any null elements.)

     *

     * <p>Like the {@link #toArray()} method, this method acts as bridge between

     * array-based and collection-based APIs.  Further, this method allows

     * precise control over the runtime type of the output array, and may,

     * under certain circumstances, be used to save allocation costs.

     *

     * <p>Suppose {@code x} is a list known to contain only strings.

     * The following code can be used to dump the list into a newly

     * allocated array of {@code String}:

     *

     * <pre>

     *     String[] y = x.toArray(new String[0]);</pre>

     *

     * Note that {@code toArray(new Object[0])} is identical in function to

     * {@code toArray()}.

     *

     * @param a the array into which the elements of the list are to

     *          be stored, if it is big enough; otherwise, a new array of the

     *          same runtime type is allocated for this purpose.

     * @return an array containing the elements of the list

     * @throws ArrayStoreException if the runtime type of the specified array

     *         is not a supertype of the runtime type of every element in

     *         this list

     * @throws NullPointerException if the specified array is null

     */

    @SuppressWarnings("unchecked")

    public <T> T[] toArray(T[] a) {

        if (a.length < size)

            a = (T[])java.lang.reflect.Array.newInstance(

                                a.getClass().getComponentType(), size);

        int i = 0;

        Object[] result = a;

        for (Node<E> x = first; x != null; x = x.next)

            result[i++] = x.item;


        if (a.length > size)

            a[size] = null;


        return a;

    }


    private static final long serialVersionUID = 876323262645176354L;


    /**

     * Saves the state of this {@code LinkedList} instance to a stream

     * (that is, serializes it).

     *

     * @serialData The size of the list (the number of elements it

     *             contains) is emitted (int), followed by all of its

     *             elements (each an Object) in the proper order.

     */

    private void writeObject(java.io.ObjectOutputStream s)

        throws java.io.IOException {

        // Write out any hidden serialization magic

        s.defaultWriteObject();


        // Write out size

        s.writeInt(size);


        // Write out all elements in the proper order.

        for (Node<E> x = first; x != null; x = x.next)

            s.writeObject(x.item);

    }


    /**

     * Reconstitutes this {@code LinkedList} instance from a stream

     * (that is, deserializes it).

     */

    @SuppressWarnings("unchecked")

    private void readObject(java.io.ObjectInputStream s)

        throws java.io.IOException, ClassNotFoundException {

        // Read in any hidden serialization magic

        s.defaultReadObject();


        // Read in size

        int size = s.readInt();


        // Read in all elements in the proper order.

        for (int i = 0; i < size; i++)

            linkLast((E)s.readObject());

    }


    /**

     * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>

     * and <em>fail-fast</em> {@link Spliterator} over the elements in this

     * list.

     *

     * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and

     * {@link Spliterator#ORDERED}.  Overriding implementations should document

     * the reporting of additional characteristic values.

     *

     * @implNote

     * The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}

     * and implements {@code trySplit} to permit limited parallelism..

     *

     * @return a {@code Spliterator} over the elements in this list

     * @since 1.8

     */

    @Override

    public Spliterator<E> spliterator() {

        return new LLSpliterator<E>(this, -1, 0);

    }


    /** A customized variant of Spliterators.IteratorSpliterator */

    static final class LLSpliterator<E> implements Spliterator<E> {

        static final int BATCH_UNIT = 1 << 10;  // batch array size increment

        static final int MAX_BATCH = 1 << 25;  // max batch array size;

        final LinkedList<E> list; // null OK unless traversed

        Node<E> current;      // current node; null until initialized

        int est;              // size estimate; -1 until first needed

        int expectedModCount; // initialized when est set

        int batch;            // batch size for splits


        LLSpliterator(LinkedList<E> list, int est, int expectedModCount) {

            this.list = list;

            this.est = est;

            this.expectedModCount = expectedModCount;

        }


        final int getEst() {

            int s; // force initialization

            final LinkedList<E> lst;

            if ((s = est) < 0) {

                if ((lst = list) == null)

                    s = est = 0;

                else {

                    expectedModCount = lst.modCount;

                    current = lst.first;

                    s = est = lst.size;

                }

            }

            return s;

        }


        public long estimateSize() { return (long) getEst(); }


        public Spliterator<E> trySplit() {

            Node<E> p;

            int s = getEst();

            if (s > 1 && (p = current) != null) {

                int n = batch + BATCH_UNIT;

                if (n > s)

                    n = s;

                if (n > MAX_BATCH)

                    n = MAX_BATCH;

                Object[] a = new Object[n];

                int j = 0;

                do { a[j++] = p.item; } while ((p = p.next) != null && j < n);

                current = p;

                batch = j;

                est = s - j;

                return Spliterators.spliterator(a, 0, j, Spliterator.ORDERED);

            }

            return null;

        }


        public void forEachRemaining(Consumer<? super E> action) {

            Node<E> p; int n;

            if (action == null) throw new NullPointerException();

            if ((n = getEst()) > 0 && (p = current) != null) {

                current = null;

                est = 0;

                do {

                    E e = p.item;

                    p = p.next;

                    action.accept(e);

                } while (p != null && --n > 0);

            }

            if (list.modCount != expectedModCount)

                throw new ConcurrentModificationException();

        }


        public boolean tryAdvance(Consumer<? super E> action) {

            Node<E> p;

            if (action == null) throw new NullPointerException();

            if (getEst() > 0 && (p = current) != null) {

                --est;

                E e = p.item;

                current = p.next;

                action.accept(e);

                if (list.modCount != expectedModCount)

                    throw new ConcurrentModificationException();

                return true;

            }

            return false;

        }


        public int characteristics() {

            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;

        }

    }


}

